Cadmium coating



Patented F b. 10, 1942 canmom-cos'rmc y Georg Renter, Markranstadt, near Leipzig.

No Applieationliecember zo,1'9a9,se-

rial No. 310,145. In Germany'Apl-il 27 1937 This invention relates to the deposition of it the bath-containslargeexcessive amounts of coatings of cadmiumwithout application oikan outside source of current, by way oi aqueous solutions 01 cadmium salts.

The process of depositing e. g. silver, copper or. tin as metal coatings in a .simple and economical manner according to the so-called immersion or hot bathprocess, without application oi any outside source of electric current, is'wvell known. It isalso possible to produce nickel and brass deposits in the same manner. Greatdifllculties have been encountered, however, in the deposition of zinc or cadmium from aqueous solutions without application 0! any outside source of electriccurrent. It has been suggested to produce metal coatings of cadmium on aluminum by dipping cleaned parts of aluminum into a solution of complex cadmium-cyanide previously heated to 60 C. This, however, yields only a very thin coating which does not ofier any efli cient protection. It has further been-suggested to produce metal deposits on ironby boiling with a mixed solution of cadmium salt and tin-salt.

It has been found, however, that by means of such a solution the deposition oi pure cadmiumis not possible.

It is the object of the '.present invention to provide a system of depositing adherent coatings of cadmium upon other metals, withoutapplication of any outside source of electric current, from aqueous solutions of cadmium salts, i. e.,

of at least the same thickness, as is,possible with silver or tin. According to the invention,

the articles to be coated are treated in potassium cyanide solutions or alkali solutions of cadmiumsalt which show an excess of freealkalLcyanides or caustic alkali many times that of the dissolved cadmium metal. The cadmium coating may be deposited, e. g., on copper, brass, copper plated or brass plated iron, but also directly on iron. The coating is most easily formed in an'adherent and brilliant form on surfaces or alloys like brass.

Cyanogen-cadmium baths are well known in galvano-technics, which for attainingbright and brilliant coatings'by application of electric current contain a certain excess oi caustic soda and cyanide of sodium. Such baths, mowever,

I cannot be used in connection with a hot treatment without electric current. Moreover, it has alkali cyanides or caustic alkali in relation to the cadmium dissolved.

According to the invention the production of um coatings directly upon' blank iron,. can be attained by boiling the 'articlesin very hot fbaths at-temperature'sexceeding 100 C. Such temperatures according to the'invention, can be made possible by a considerable admixture of soda or by a heavy increase of the'amount of free, excessive caustic alkali in the. contents of the bath. Some alkali cyanidecan also be. provided, it available. 'Provided that sufficiently high temperatures are attained, the direct coating of blank iron with cadmium does not offer any difilculties. The cadmium is deposited in an adherent .iorm, which can be easily polished and oflers good protection against corrosion. With,

certain sorts oi iron the coating with cadmium is facilitated by a previous short pickling treatment with mineral acids or similar, acids.

For the deposition of cadmium coatings on articles made of brass, according tothe invention, the bathcan be composed as follows: v

About 4 grams cadmium in the form of its oxide, chloride. carbonate or in some other form of salt. About?!) to 150 grams alkali cyanide, 1000'grams water, temperature: 40 to 70 C.

For depositing cadmium coatings on blankerence but is broader in scope and capable of,

other embodiments than those specifically described.-

I claim:

' l. A process of producing adherent coatings of cadmium to be deposited'on a metal of the group consisting of copper, brass, iron, copper.-

plated iron, and brass plated iron, without the application of an outside source of electric current, by' means of a hot bath treatment, in which the articles to be coated are treated in hot aqueous alkali cadmium salt solutions which contain an excess of free caustic alkali many times by weight that oi'the dissolved cadmium metal.

55 it. A" process ofproducing adherent coatings of cadmium on a metaloi the group consisting of copper,-brass. iron, copper-plated iron, and

brass plated iron, without application 01 an outside source of electric current, by means 01a hot bath-treatment, in which the articles to be coated are treated'in hot aqueous alkali cadmium salt solutions which'contain an excess of iree times by weight that of the dissolved cadmium metal.

; 4. A-processfor the production of adherent coatings of-cadmium on a metal 01 .the group consisting of copper, brass, iron, copper-plated iron, and brass plated iron without application of an outside source of electric current, by means of a hot bath treatment, in which the articles to be coated are treated in hot aqueous potassium cyanide solutions of cadmium salt which contain an excess of free caustic alkali many times by welghtithat of the dissolved cadmium metal.

5. A process for the production of adherent coatings of cadmium on iron, without application of an outside source of electric current. by means of a boiling treatment, in which the articles to be coated are treated in aqueous solutions oi the group consisting of potassium cyanide solutions and alkali solutions of cadmium salts which'contain an excess of alkali oi the group consisting of alkali cyanides and caustic alkali manytimes by weight that of the dissolved cadmiurn metal and in which the boiling treatment is carried out at a temperature exceeding 100 C.

, '6. A process for the production of adherent coatings'of cadmium on iron without application of an outside source of electric current, by means 0! a boiling treatment, inwhich the articles to be coated are treated in aqueous cadmium salt solutions of the group consisting of potassium cyanide solutions and alkali solutions of cadmium salts which contain an excess of alkali oi the group consisting of alkali cyanides and caustic alkali many times by weight that of the dissolved cadmium metal and in whichthe boiling treatment is carried out at a temperature eit-v acceding 100 0., this temperature being made possible by a heavy addition to the bath of an alkali of the group consisting of soda and caustic alkali. a

'7. A process for the production of an adherent coating oi cadmium on brass without application of an outside source of electric current, by means of a hot bath treatment in which the articles to be coated are treated in a' solution of approximately four parts by weight of a substance selected irom the group consisting of the oxide and the salts of cadmium, between 70 and 150 parts by weight of an alkali cyanide in 1000 parts by weight of water at a temperature between 40 to C. 8. A process for the production 01' an adherent coating of cadmium on blank iron without application of an outside source of electric current by means of a boiling treatment, in which the articles to be coated are treated in a bath containing between 5 and 8 partsby weight of a substance selected from the group consisting of the oxide and the salts of cadmium, between 1200 and 1400 parts by weight of a caustic alkali, 

